Method for producing a sulfonated polyarylether block copolymer

A method for producing a sulfonated polyarylether block copolymer, said copolymer comprising a hydrophobic segment having a structural unit represented by formula (5) and a hydrophilic segment having a structural unit with sulfonic acid groups or derivative thereof incorporated into a structure represented by formula (6),

• wherein,
• D1 is SO2 or CO;
• and
• Ar1 is a divalent aromatic residue bonded to an electron-withdrawing group in every aromatic ring belonging to Ar1,
• wherein,
• D2 of formula (6) is SO2 or CO;
• and
• Ar2 is a divalent aromatic residue,
• the method comprising block copolymerizing a hydrophilic segment prepolymer represented by formula (18) and a hydrophobic segment prepolymer, the block copolymerization being conducted through ether exchange reaction,
• wherein
• D2 of formula (18) is SO2 or CO;
• Ar2 is a divalent aromatic residue;
• a is an integer of from 20 to 1,000;
• p and q are independently an integer of 0, 1 or 2;
• and
• p+q≧1,
• wherein the hydrophilic segment prepolymer is prepared from a 3,3′-disulfo-4,4′-dichlorodiphenylsulfonate, and
• wherein the sulfonated polyarylether block copolymer has an ion-exchange capacity of 0.5 mmol/g to 3.0 mmol/g.